Conventionally, a sensor or a camera mounted on an automobile is used to detect an approaching vehicle based on its output. In most cases, presence/absence of the approaching vehicle is detected by pattern matching between features extracted from captured images and templates prepared in advance. For example, Japanese Patent No.3014233 discloses an approaching object detecting apparatus. According to the apparatus, a captured image is divided into a plurality of window regions. A pattern corresponding to the image is created with features extracted from each window region as a data array. By comparing the pattern with the captured image, the approaching object apparatus may be detected automatically and reliably.
Various methods may be used to extract features from the captured image. Among those, many methods use optical flows. For example, Japanese Patent No.3011566 discloses an approaching vehicle monitoring apparatus. According to the apparatus, optical flows are computed based on captured images. By detecting a moving object and its movement direction through the use of the optical flows, only approaching vehicle may be detected separately from its background. Since optical flows are used to eliminate noise according to this invention, more accurate detection may be realized.
There are some techniques for not only detecting the approaching vehicle by image processing but controlling the vehicle by utilizing the result of the image processing. For example, Japanese Unexamined Patent Publication (Kokai) No.2001-101592 discloses a vehicle collision prevention apparatus. By detecting conditions of an intersection before entering it, the apparatus takes an appropriate action to avoid collision. If it is determined that collision avoidance action is necessary, the apparatus instructs the vehicle to make a braking or temporarily prohibit the driver's pressing of an accelerator pedal.
In order to detect the approach of another vehicle based on an image, pattern matching is necessary between the image and templates. However, if the templates should be prepared in advance, a large number of templates are required to make an appropriate vehicle control in many different situations. This may cause a problem of storage capacity.
There may be much difference between scenes on which the driver determines that collision avoidance action is needed depending on some information such as road conditions, weather and the driver's personal character. Therefore, if the number of templates for determination is limited, flexibility is lost and collision avoidance action can be made in inappropriate condition, which makes a bad effect on driving.
Therefore, there is a need for vehicle control system which is flexibly applicable to driver's characteristics and various situations around the primary vehicle with relatively small storage capacity.